The Lambkins by Eve Bunting

The story begins, "It was 8:30 on a warm California night when the woman kidnapped me." 

Kyle, a high school student, stops to help an old woman change a flat tire.  Before he knows what's happened, she pushes him in the trunk of her car and injects him with some weird formula.  When he wakes up, he's the size of a miniature doll, and finds himself living in a dollhouse with other kids who have been shrunken to doll size.  They are part of Mrs. Shepherd's "collection."   She says she loves them like her own children and she'd never harm them – unless, of course, they make her angry.

John made her angry.  Look what happened to him.   

You'll have to read the book The Lambkins by Eve Bunting to find out.